Sleepy device operation in asynchronous channel hopping networks

ABSTRACT

A radio communications device includes a RTC configured to run even during sleep for receiving from a coordinator node (CN) in an asynchronous channel hopping WPAN an asynchronous hopping sequence (AHS) frame that includes the CN&#39;s hopping sequence. A processor implements a stored sleepy device operation in asynchronous channel hopping networks algorithm. The algorithm is for determining a time stamp for the AHS frame and the CN&#39;s initial timing position within the hopping sequence, storing the time stamp, going to sleep and upon waking up changing a frequency band of its receive (Rx) channel to an updated fixed channel. A data request command frame is transmitted by the device on the CN&#39;s listening channel that is calculated from the CN&#39;s hopping sequence, time stamp, CN&#39;s initial timing position and current time, and the device receives an ACK frame transmitted by the CN at the updated fixed channel of Rx operation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application and the subject matter disclosed herein claims thebenefit of Provisional Application Serial No. 62/327,794 entitled “SleepMode Operation In Un-slotted Channel Hopping Networks” filed Apr. 26,2016, which is herein incorporated by reference in its entirety.

FIELD

Disclosed embodiments relate generally to wireless personal areanetworks, and more particularly to asynchronous (un-slotted) channelhopping in such networks.

BACKGROUND

IEEE 802.15.4e is an enhanced media access control (MAC) layer protocolof IEEE 802.15.4 designed for low power and low data rate networks. TheIEEE 802.15.4e architecture is defined in terms of a number of blocks inorder to simplify the standard. These blocks are called layers. Eachlayer is responsible for one part of the standard and offers services tothe higher layers. The interfaces between the layers serve to define thelogical links that are described in the standard. A low-rate(LR)-Wireless personal area network (WPAN) device comprises at least onePHY (physical layer), which contains the radio frequency (RF)transceiver along with its low-level control mechanism, and a mediumaccess control (MAC) sublayer that provides access to the physicalchannel for all types of transfers.

IEEE 802.15.4e is suitable for sensor devices with resource constraints;e.g., low power consumption, low computation capabilities, and lowmemory. As sensors and actuators that are interconnect by a personalarea network (PAN) in home and office environments become more common,limiting power dissipation of each device is important. Some devices mayoperate on a battery, in which case frequent battery changes areundesirable. Some devices may operate on a limited amount of power thatis generated by the device itself such as using conversion from solar orother light sources, scavenging from motion or thermal effects, orcollection of energy from ambient electromagnetic fields.

Channel hopping is known for improving network capacity. Channel hoppingcan be achieved by a variety of different methods. The two most commonknown hopping methods are a synchronous method called Time SlottedChannel Hopping (TSCH) and an asynchronous channel hopping methoddefined in IEEE 802.15.4e. Many standards also exist that use such achannel hopping MAC to define MAC protocols for different applications.For example the Wi-SUN™ Alliance has published a Field Area Network(FAN) specification that specifies how to use asynchronous channelhopping for smart grid applications.

In TSCH, the time is divided into time slots, and every network deviceis time-synchronized to a root node in the network and uses the timeslots to communicate/synchronize in the network. The device hops amongall channels according to a frequency hopping sequence (FHS) during thetime slots. TSCH can achieve higher capacity and provide finergranularity for power savings in IEEE 802.15.4e networks.

In asynchronous channel hopping networks, nodes hop to differentchannels (frequency bands) in a globally unsynchronized manner. Thenodes in such networks must therefore always stay awake to enablechannel hopping for achieving increased network throughput by promotingsimultaneous data transfer over multiple channels between differentpairs of nodes, or to achieve reliability in tough channel conditions byexploiting the channel diversity.

WPANs are used to convey information over relatively short distances.Unlike wireless local area networks (WLANs), connections effected viaWPANs involve little or no infrastructure. This feature allows small,power-efficient, inexpensive network solutions to be implemented for awide range of devices. Two different device types can participate in anIEEE 802.15.4 network include a full-function device (FFD) and areduced-function device (RFD). An FFD is a device that is capable ofserving as a personal area network (PAN) coordinator. An RFD is a devicethat is not capable of serving as a PAN coordinator. An RFD is intendedfor applications that are simple, such as a light switch or a passiveinfrared sensor that does not have the need to send large amounts ofdata and to only associate with a single FFD at a time. Consequently,the RFD can be implemented using minimal resources and memory capacity.

Although IEEE 802.15.4 supports asynchronous channel hopping networks,it does not disclose or suggest a solution for sleepy node deviceoperation in such networks. Because sleepy nodes are required to go intoa low power state where they are not be able to maintain their hoppingsequence, this requires the sleepy node devices in the IEEE 802.15.4network to therefore always stay awake to support channel hoppingoperation.

SUMMARY

This Summary is provided to introduce a brief selection of disclosedconcepts in a simplified form that are further described below in theDetailed Description including the drawings provided. This Summary isnot intended to limit the claimed subject matter's scope.

Disclosed embodiments are directed, in general, to communications and,more specifically, to methods of sleepy node radio communication device(SN) operation in asynchronous (or unslotted) channel hopping networks.Disclosed embodiments utilize a combination of pseudo-channel hopping atthe SN regular asynchronous channel hopping at the non-sleepycoordinator node radio device (CN) for star (or tree)-based networks,where the SNs talk to the non-sleepy CN (parent) and do not support anychildren nodes of their own.

In disclosed embodiments the SN obtains the hopping information it needsto track the CN's channel as specified in a wireless communicationsstandard such as the Wi-SUN™ standard. Using only the time differencebetween the last received frame from CN (t₁ shown in FIG. 2B describedbelow) and time of transmission of the frame (Δt shown in FIG. 2Bdescribed below) from the SN (irrespective of the length of time of apotential sleep for the SN in between), the SN keeps track of its CN'shopping. The SN can always change its Rx channel and will convey itscurrent Rx channel information to the CN by adding it to a data requestcommand frame.

The SN can include a hardware real time clock (RTC) that remains ON evenduring sleep, and the SN is allowed to go to sleep, for generally asleep time that spans more than one sequential frame. The SN later wakesup from sleep and changes a frequency band of its receive (Rx) channelto an updated fixed Rx channel of operation, and then can exchange itsupdated Rx channel in a poll request (a data request frame) to its CN.The SN receiving a hopping sequence frame from the CN along with timinginformation from its RTC (or another clock) and the hopping sequenceframe allows the SN to keep track of CN's hopping schedule even acrosssleep periods. This enhances IEEE 802.15.4 sleep mode operation to nowallow SNs the feature of sleep mode operation in an asynchronous channelhopping network (ACHN).

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, wherein:

FIG. 1 shows operational steps in a known IEEE 802.15.4 indirecttransmission procedure where the SN is shown as an RFD and the CN as aPAN coordinator.

FIG. 2A is a flowchart and FIG. 2B an accompanying associated timelinefor an example method of SN device operation in ACHN communications,according to an example embodiment.

FIG. 3 is a block diagram schematic of an example asynchronous channelhopping (ACH) device having a disclosed communications device having aSN side ACHN operation algorithm, according to an example embodiment.

FIG. 4 shows operational steps in a detailed specific embodiment for SNoperations in an ACHN, according to an example embodiment.

DETAILED DESCRIPTION

Disclosed embodiments now will be described more fully hereinafter withreference to the accompanying drawings. Such embodiments may, however,be embodied in many different forms and should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of this disclosure to those having ordinaryskill in the art. One having ordinary skill in the art may be able touse the various disclosed embodiments and there equivalents.

In known art, IEEE 802.15.4 provides a method called indirecttransmission that is used in a message exchange between a SN andnon-sleepy CN (or parent node). FIG. 1 shows operational steps in thisknown IEEE 802.15.4 indirect transmission procedure (marked prior art)where the SN is shown as an RFD 110 and the CN as a PAN coordinator 120.

SNs are a special type of RFD 110 which can turn their receiver offduring idle times to conserve electrical power. SNs go into a low powerstate during sleep where they are not be able to transmit or receive anyframes. In order for SNs such as RFD 110 to participate in a networkoperation, the SN conventionally performs the following steps that areshown in FIG. 1.

Step 1. First scanning for an available network using a beacon-basedactive or a passive scan procedure shown as a beacon request 111.

Step 2. After receiving at least one beacon from the PAN coordinator120, the RFD 110 performs an association procedure by sending theassociation request 112a shown during which it indicates its capabilityas a SN to the PAN coordinator 120 and then the RFD 110 sends a datarequest command frame shown as a MAC data request 112 b to the PANcoordinator 120.

Step 3. The PAN coordinator 120 responds using an association responsemessage 113 stating whether it accepts to operate with such a SN.

Step 4. Upon a successful association concluded with the associationresponse message 113 where the PAN coordinator 120 acceptscommunications with the RFD 110, and the RFD 110 sends anacknowledgement (ACK), and the data exchange between the PAN coordinator120 and the RFD 110 occurs as follows:

The RFD 110 can transmit data to the PAN coordinator 120 at any timebecause the PAN coordinator 120's receiver is always ON. The RFD 110sends a MAC data poll to the PAN coordinator 120. After sending a MACACK 114 a to the RFD 110, the PAN coordinator 120 transmits a data frame114 b using indirect transmission to the RFD 110 where the MAC ACK 114 abuffers the data frame 114 b for the RFD 110. The RFD 110 polls for datafrom the PAN coordinator 120 whenever it wakes up from sleep mode usingthe MAC data request 112 b. The PAN coordinator 120's MAC then transmitsthe data frame 114 b to RFD 110.

However, it is recognized this known method for SNs to participate inPAN operation cannot be directly applied to the FAN specification. Thisis because SNs such as RFD 110 cannot asynchronous channel hop due tothe following three (3) reasons that make implementation of asynchronouschannel hopping not possible:

1. The Wi-SUN™ FAN specification does not natively support the IEEEcommand frames for association and indirect transmission.

2. A SN such as RFD 110 does not keep track of the PAN coordinator 120'scurrent receiver channel after a sleep operation. In this ACH mode, thePAN coordinator 120's hops on different receive channels. The onus is onthe SN (such as RFD 110) transmitter to send the packet on the rightreceive channel so that the PAN coordinator 120 can receive it. Hence,the SN (such as RFD 110) being the transmitter of the data requestcommand (MAC data request 112 b) is unable to keep track of the hoppingsequence of the PAN coordinator 120.

3. The SN such as RFD 110 does not keep track of its unicast hoppingsequence during sleep.

According to Wi-SUN™ FAN every device node has to keep track and hop onits own sequence and the transmitter shall then use the same sequence todetermine its receive channel when initiating the transmissions. Ascheme to maintain the PAN coordinator 120's hopping sequence acrosssleep operation for a SN such as RFD 110 could thus require maintenanceof dwell intervals during sleep states which could hamper the level towhich a SN can go to sleep (and thus raise the power it consumes).

Disclosed embodiments use the below-described communication sequence tosolve each of the above-described three reasons that make implementationnot possible for SNs to operate in ACHNs. The ACHN as defined in Wi-SUN™does not allow for exchange of IEEE command frames which would allow forcommand frames to be supported for association and indirecttransmission. In order for the SN to keep track of a non-sleepy CN'shopping schedule, the SN can have a real-time clock (RTC) that stays oneven during sleep, and the SN can store the time stamp of the lastreceived frame from the CN in terms using its RTC (or another clock).When the SN intends to transmit a frame to CN, it computes thedifference in time based on the RTC and then can use the UnicastFractional Slot Interval (UFSI) being the field that contains the timinginformation of the node's current position in its hopping sequence, fromthe last received frame from the CN to compute the CN's current receivechannel.

This implies that a SN should not go to low power mode for more than theRTC's wraparound time. Wrap around times are implemented as some numberof bytes of data, such as 4 bytes, then it only stores a maximum valuesuch as 2³², any time after that shall wraparound to 0 and continue. Itis recommended that the SN does not go back to low power mode withoutreceiving updated timing information from the CN or wake up multipletimes within a wraparound period to perform the data request operation.

The requirement to maintain a SN's own hopping schedule across sleepoperation would complicate the design of SNs they would now have to keeptrack of their sleep times accurately. To overcome this limitation andsolve this problem, disclosed SNs use a fixed channel of Rx operation.However, to achieve a change in listening (Rx) frequency the SNs changethe fixed channel of Rx operation each time they wake up. In order forthe CN to know the updated fixed channel of Rx operation in which the SNoperates, the SN advertises (carries) its fixed channel of Rx operationin its data request command by including a unicast schedule. The CN isthen able to use this newly updated channel information to transmit theindirect frame over the correct channel to the SN.

Disclosed methods of SN operation in ACHNs thus utilize a combinationof:

1. Pseduo-channel hopping at the SN where the Rx channel is changedbefore Tx of a data request command frame either by application, higherlayer or MAC, using any hopping sequence. Such an hopping sequence neednot be exchanged to the CN as any time the CN wants to send a frame tothe SN it has happened after the receipt of a data request command whichcontains the current Rx channel of the SN.

2. The asynchronous receive channel hopping sequence of the CN devicebased on some standard hopping sequence is exchanged to the SN throughinformation elements (IE) in an asynchronous frame (PANAdvertisement/PAN Configuration frames). The SN can use this exchangedhopping sequence and the time stamps to determine the channel at whichthe CN device is currently listening.

FIG. 2A is a flowchart and FIG. 2B an accompanying associated timelinefor an example method 200 of SN operation in a WPAN having a CN,according to an example embodiment. As described below method 200enables the SN to change a frequency of its Rx channel without actuallyperforming any hopping.

Step 201 comprises the SN receiving from the CN an AHS frame thatincludes the CN's hopping sequence and the CN's initial timing positionwithin the hopping sequence. The CN's timing position within the hoppingsequence can be based on timing information included within the AHSframe or in another communication received from the CN (e.g., from lastreceived data from the CN or an ACK frame from the CN). The SN caninclude a RTC configured to run even during sleep mode operation thatgenerates a time stamp from the AHS frame reflecting a time which theAHS frame from the CN was received.

In the FIG. 2B timeline, at a time shown as 251, the CN transmitsframe(s) along with additional information as information elements(IE)s. IE are a MAC frame ‘unit’ which can be used to carry additionalinformation apart from payload data. A special IE which may be called atiming IE, is generally used by the CN in the AHS frame in step 201 tocarry the timing information of its current position within its hoppingsequence at that time. The time at 251 is shown as being Δt from somereference time that is shown in FIG. 2B as being time 0. At Δt the CN isshown being at CH 2.

Step 202 comprises the SN storing the time stamp and the CN's initialtiming position (e.g., as reported inside the AHS frame), then going tosleep. The time stamp as noted above can be provided by a RTC generallyat the SN.

Step 203 comprises the SN waking up from the sleep and then changing afrequency band of its Rx channel to an updated fixed channel of Rxoperation. For example, in the United States, the 902-928 MHz band canbe split into 129 200 KHz wide channels, any of which can be used by theSN for the Rx channel. In the FIG. 2B timeline, the CN sleeps for aperiod of time=t₁.

In step 204, the SN transmits a data request command frame at a channelcorresponding to the CN's current listening channel calculated from (i)the CN's hopping sequence, (ii) the time stamp, (iii) the CN's initialtiming position, and (iv) a current time (e.g., current time obtainedfrom the SN's RTC, see RTC 304 in FIG. 3 described below). Optionally,the data request command frame can include additional payloadinformation including the updated fixed channel of Rx operation to theCN for advertising the updated fixed channel of Rx operation to the CN.The CN's calculated current listening channel is shown in FIG. 2B asbeing CH 4. The data request command frame is transmitted as a unicasttransmission. In the FIG. 2B timeline, at a time shown as 252, the SNtransmits a frame to the CN at the CN's current listening channel (CH 4)shown calculated as (t1+Δt)/DT. DT stands for dwell time, being theamount of time a node stays on a given channel before moving to nextchannel.

Step 205 comprises the CN transmitting an ACK frame at the updated fixedchannel of Rx operation to the SN. Following step 205, the CN cantransmit data at the updated fixed channel of Rx operation to the SN(thus on the same channel as the ACK frame), followed by the SNtransmitting data at the CN's current listening channel to the CN.

In an alternate embodiment, the updated fixed channel of Rx operationselected by the SN after it wakes up is set to the CN's listening (Rx)channel at the time of the SN transmitting the data request command(calculated by the SN to transmit the data request command frame in step204). In yet another alternate embodiment, the CN implicitly‘understands’ that the updated fixed channel of Rx operation of the SNis the same channel on which the CN received the data request commandframe without the need of explicitly exchanging identification of the Rxchannel of operation of the SN over the data request command frame. Inthis embodiment, the SN does not ‘append’ its listening (Rx) channel tothe data request command frame. Instead the CN understands that the SNwill be listening for a response from the CN in that same channel atwhich the CN had received the data request command frame.

Advantages of disclosed SN operation in ACHNs include:

1. being compatible with current operation of Wi-SUN™ un-slotted channelhopping mechanism;

2. not posing any strict timing requirement on either the SN or the CN;

3. the SN does not need to keep track of its hopping sequence, and

4. allows for the use of any implementation specific hopping sequence onSN.

FIG. 3 is a block diagram schematic of an example SN 300 having adisclosed SN side ACHN operation algorithm 303 a. The CN does not needany change(s) to implement disclosed SN device operation in asynchronouschannel hopping networks, but should support the indirect transmissionssuch as defined in IEEE 802.15.4, and include a RTC. SN device 300 mayinclude a system processor (system CPU) 301 that includes a nonvolatilememory 303 (e.g., static random-access memory (SRAM)) for holdinginstructions and data. Nonvolatile memory 303 may store software programinstructions that may be executed by the system CPU 301 and/or thetransceiver 302 to perform some or all of the network functionsdescribed herein, for example running the ACHN operation algorithm 303a. SN 300 is also shown implementing a wakeup handler block 310 whichperforms the necessary state transition steps 311 (e.g., radio setup)and MAC software block 312. Functions for 310-312 may be performed bysoftware executed on the system CPU 301. SN 300 is shown powered by abattery 323. One or more sensors 306 and/or one or more actuatorcircuits 308 may be included in SN 300 for interacting with the physicalworld.

A bus 327 couples together the respective components of SN 300.Transceiver 302 is coupled to the antenna 319. A hardware RTC 304 isincluded in SN 300 that is provided to the system CPU 301.

Disclosed subject matter can be used in a variety of applications. Oneapplication has a plurality of disclosed SNs including a sensor 306 oran actuator 308. In this embodiment the WPAN is part of a smart gridthat can comprise an electricity supply network which uses digitalcommunications to detect and react to local changes in electrical usage.Other example uses include industrial automation and home automation.

EXAMPLES

Disclosed embodiments are further illustrated by the following specificExamples, which should not be construed as limiting the scope or contentof this Disclosure in any way.

FIG. 4 shows operational steps in a detailed specific embodiment for SNoperations in an ACHN, according to an example embodiment. The SN inFIG. 4 is shown as RFD 110′ and the CN as a PAN coordinator (PC) 120.The RFD 110′ sends an association request 411 during which it indicatesits capability as a SN to the PC 120. After receiving an ACK 412 fromthe PC 120 the RFD 110′ sends a MAC data request 413. After a MAC ACK414, the PC 120 transmits an association response which is an AHS framealong with an IE that corresponds to step 201 in method 200 whichincludes the PC's hopping sequence and the PCs initial timing positionwithin the hopping sequence. The asynchronous Rx channel hoppingsequence of the PAN coordinator (based on a standard hopping sequence)is provided to the RFD 110′ and the timing information of its positionwithin its hopping sequence through IEs in this AHS frame. The RFD 110′stores the time stamp for the AHS frame and the PC's timing position,then goes to sleep for generally a time corresponding to more than oneframe.

Upon wakeup, the RFD 110′ sets its frequency band of its Rx channel to afirst updated fixed channel of Rx operation shown as Fl. The RFD 110′transmits a data request command frame (shown as step 204′) to the PC120 at a channel corresponding to the PC's 120 current Rx channelcalculated from the CN's hopping sequence, the time stamp, the CN'sinitial timing position and a current time (e.g., from its RTC). Inresponse the PC 120 transmits an ACK frame (shown as step 205′) at theupdated fixed channel of Rx operation of the RFD 110′ (here Fl) to theRFD 110′. The PC 120 then transmits data (step 206′) at Fl to the RFD110′.

After sending an ACK, the RFD 110′ again goes to sleep, and upon wakeupthe RFD 110′ sets its frequency band of its Rx channel to a secondupdated (new) fixed channel of Rx operation shown as F2. The RFD 110′transmits a data request command frame (shown as step 204″) to the PC120 at a channel corresponding to the PC's 120 current Rx (listening)channel calculated from the CN's hopping sequence that is stored frombefore, the time stamp, the CN's initial timing position and a currenttime (e.g., from the RTC). In response the PC 120 transmits an ACK frame(shown as step 205″) at the updated fixed channel of Rx operation of theRFD 110′ (here F2) to the RFD 110′. The PC 120 then transmits data (step206″) at F2 to the RFD 110′.

Many modifications and other embodiments will come to mind to oneskilled in the art to which this Disclosure pertains having the benefitof the teachings presented in the foregoing descriptions, and theassociated drawings. Therefore, it is to be understood that embodimentsof the invention are not to be limited to the specific embodimentsdisclosed. Although specific terms are employed herein, they are used ina generic and descriptive sense only and not for purposes of limitation.

1. A method of operating a sleepy node communications radio device (SN)in an asynchronous channel hopping wireless personal area network (WPAN)having a coordinator node radio device (CN), comprising: said SNreceiving from said CN an asynchronous hopping sequence frame (AHSFrame) that includes at least said CN's hopping sequence and said CN'sinitial timing position within said hopping sequence from said AHS Frameor another frame received from said CN; said SN storing a time stamp andsaid CN's timing position, then going to sleep; said SN waking up fromsaid sleep and then changing a frequency band of its receive (Rx)channel to an updated fixed channel of Rx operation; said SNtransmitting a data request command frame at a channel corresponding tosaid CN's current listening channel calculated from said CN's hoppingsequence, said time stamp, said CN's initial timing position and acurrent time, and receiving an acknowledgement (ACK) on the samechannel; said CN transmitting a response frame at said updated fixedchannel of Rx operation to said SN.
 2. The method of claim 1, whereinsaid SN uses an included hardware real-time clock (RTC) configured torun even during sleep mode operation to keep track of said CN's hoppingsequence.
 3. The method of claim 1, wherein said data request commandframe further comprises payload information including said updated fixedchannel of Rx operation to said CN.
 4. The method of claim 1, whereinsaid time stamp is determined from last received data from said CN orfrom said AHS frame.
 5. The method of claim 1, wherein said CN's timingposition within said hopping sequence is based on timing informationincluded in said AHS frame.
 6. The method of claim 1, further comprisingsaid CN transmitting data at said updated fixed channel of Rx operationto said SN.
 7. The method of claim 6, further comprising said SNtransmitting data at said CN's current listening channel to said CN. 8.The method of claim 1, wherein said SN includes a sensor or actuator,and wherein said WPAN is part of a smart grid that comprises anelectricity supply network which uses digital communications to detectand react to local changes in electrical usage.
 9. The method of claim1, wherein said updated fixed channel of Rx operation is set to saidchannel corresponding to said CN's current listening channel.
 10. Themethod of claim 1, wherein said CN implicitly understands said updatedfixed channel of Rx operation is said channel corresponding to said CN'scurrent listening channel or as a function of said channel correspondingto said CN's current listening channel.
 11. A radio communicationsdevice, comprising: a transceiver coupled to at least one antenna; ahardware real-time clock (RTC) configured to run even during sleep modeoperation for receiving from a coordinator node communications device(CN) in an asynchronous channel hopping wireless personal area network(WPAN) an asynchronous hopping sequence frame (AHS frame) that includesat least said CN's hopping sequence and said CN's initial timingposition within said CN's hopping sequence from said AHS Frame oranother frame received from said CN; a processor communicably coupled toa memory which stores a sleepy device operation in an asynchronouschannel hopping network (ACHN) algorithm including code for implementingsaid algorithm, said algorithm: determining a time stamp for said AHSFrame and said CN's initial timing position within said hoppingsequence; storing said time stamp in said memory and then going tosleep; waking up from said sleep and then changing a frequency band ofits receive (Rx) channel to an updated fixed channel of Rx operation;transmitting a data request command frame at a channel corresponding tosaid CN's current listening channel calculated from said from said CN'shopping sequence, said time stamp, said CN's initial timing position anda current time, and receiving an ACK frame transmitted by said CN atsaid updated fixed channel of Rx operation.
 12. The radio communicationsdevice of claim 11, wherein said data request command frame furthercomprises payload information including said updated fixed channel of Rxoperation to said CN.
 13. The radio communications device of claim 11,wherein said time stamp is determined from last received data from saidCN or from said AHS frame.
 14. The radio communications device of claim11, wherein said CN's timing position within said hopping sequence isbased on timing information included in said AHS frame.
 15. The radiocommunications device of claim 11, wherein said radio communicationsdevice includes a sensor or actuator and wherein said WPAN is part of asmart grid that comprises an electricity supply network which usesdigital communications to detect and react to local changes inelectrical usage.
 16. The radio communications device of claim 11,wherein said updated fixed channel of Rx operation is set to saidchannel corresponding to said CN's current listening channel.